Thrombelastography (TEG) is a diagnostic method which mechanically investigates clot formation or dissolution in an oscillating system. Here, either a vessel (cup) is in oscillating motion around a measuring rod (pin) (conventional TEG) or else the vessel is fixed and the pin is brought into oscillating rotational motion (ROTEG or ROTEM). The mechanical forces arising between the cup and pin are recorded. As soon as the blood or plasma starts to clot, a variation in the initial measurement signal occurs. Both designs will be designated here as TEG.
TEG is employed for the investigation of blood or plasma in order to determine clotting-relevant parameters (TEG parameters), such as the period of time up to reaching a first significant clot formation with an amplitude of 2 mm (clotting or reaction time r), the period of time up to reaching a clot thickness of an amplitude of 20 mm (k value), the rate at which the clot is formed (alpha angle), the mechanical properties of the clot at maximum amplitude (MA) or at any other desired point in time, the period of time up to MA (TMA), or the period of time until the clot strength has fallen again to a certain value because of fibrinolysis. Clinically, TEG is employed as a diagnostic measure, inter alia, for the assessment of coagulopathy, for example in heart surgery, in liver transplantation, major abdominal surgery and as a quasi-bedside test in perioperative clotting management (Kettner S C et al. (1999) Anesth Analg; 89: 580-584; Shore-Lesserson L et al. (1999), Anesth Analg; 88: 312-319; Harding S A et al. (1997), Br J Anaesth: 175-179; Kettner S C et al. (1998), Anesth Analg; 86: 691-695, Pivalizza E G et al. (1998), J Cardiothorac Vasc Anesth; 12: 305-308, Mahla E et al. (2001), Anesth Analg; 92: 572-577; Calatzis A N et al. (1996), Eur Surg Res; 28: S1 (89).
TEG is available in addition to the standard clotting diagnostics (inter alia Quick, aPTT, platelet count, AT III, fibrinogen, D dimers, bleeding time), which are more time-consuming for the determination of the values for rapid information about bleeding trends. This is particularly of importance if coagulopathies occur in the course of extensive surgical interventions or after polytraumata, since serious haemostasis disorders can rapidly lead to the development of secondary tissue damage and are often resistant to a conventional haemostatic therapy based on a more time-consuming standard clotting diagnosis.
The TEG parameters are influenced by a number of factors which are designated below as thrombelastographically relevant factors. Thrombelastographically relevant factors are especially fibrinogen, factor XIII, and blood platelet levels and components of the fibrinolytic system such as plasmin, plasmin activators, and plasmin inhibitors. For instance, fibrinogen, as a clotting substrate, correlates with the clot stability. This can be clearly shown in the thrombelastogram. Moreover, factor XIII likewise modulates, by means of the crosslinkage of the fibrin formed from the fibrinogen, the mechanical properties of the clot and restricts its lysis (P. Lauer et al. (2002), Thromb Haemost; 88: 97-974). The two effects have not been clearly separable from one another in thrombelastography until now, since they equally influence central measurement of a thrombelastogram. Both fibrinogen and factor XIII significantly influence the parameters clotting time (r), maximum clot strength, alpha angle as a measure of the rate of clot formation and the lysis time of the clot (Nielsen V G et al. (2004), Anesth Analg; 99: 120-123). Since in acquired deficiency states such as in polytraumata or relatively major surgical interventions the fibrinogen and the factor XIII levels do not necessarily decrease equally, up to now a selective therapeutic intervention clearly in favour of one or the other component on the basis of the thrombelastogram is not possible. It would therefore be desirable if a method was available which would allow, on the basis of rapid TEG diagnosis, a determination whether a bleeding tendency is based on a factor XIII deficiency and/or on a fibrinogen deficiency.